A problem which motivated the invention related to overcoming undesired floating body effects inherent in silicon-on-insulator field effect transistors. Such is characterized by channel region voltage inherently floating during operation, thereby affecting the threshold voltage and operation consistency of the transistor. Floating body effect typically is not an issue in bulk semiconductor circuitry, as the bulk substrate is tied or held to a specific voltage such that the substrate voltage and threshold voltage are not allowed to float. However in silicon-on-insulator field effect transistors, such does not presently occur and is particularly problematic in what are known as partially depleted silicon-on-insulator transistors. A partially depleted silicon-on-insulator transistor has its channel region only partially extending through the thickness of the silicon layer beneath the transistor gate. Factors which determine whether a field effect transistor is partially or fully depleted include the thickness of the silicon layer and the thickness of the source/drain region within the silicon layer.
Floating body effect or voltage is determined by forward current leakage to the source and reverse leakage to the drain. One known prior art method of reducing the floating body effect is to increase the source/drain junction forward bias current, thus resulting in any charge buildup in the body promptly being discharged to the source.
The following invention was motivated in addressing the above identified problems, although such is in no way so limited. The invention is limited only by the accompanying claims as literally worded without limiting reference to the specification, and in accordance with the doctrine of equivalents.